In the art of cutting eyeglass lenses it is necessary to know precisely the geometry of the lens opening within which such lenses are to be fitted. In order to measure the geometry of this lens opening the eyeglass frames must be precisely held in position, without any distortion in shape, throughout the measuring procedure. A number of prior patents have addressed this problem, vis U.S. Pat. No's. 4,049,254; 3,666,259; 3,622,144; 3,617,046 and 3,145,417 where various jigs and clamps for this purpose are discussed. These prior techniques are generally characterized by the application of clamps or restraining bars to a limited number of points e.g. 3-4, surrounding an individual lens opening. U.S. Pat. No. 3,617,046 to Sotonyl is typical in this regard.
When an eyeglass lens frame is being restrained at only a limited number of restraining points, reliance is being placed on the structural rigidity of the lens frame to ensure that the frame retains its natural shape. However, where eyeglass frames are constructed of thin rims, as in wire-rim glasses, the frame itself has significantly less structural rigidity. Where the frame is fragile, the force applied by a clamping support or jig may tend to distort its shape. Further, it is customary to extract the geometry by means of a probe which applies a slight but significant force to the edge of the rim. Even slight distortions of shape can lead to an incorrect fit for lenses intended to be mounted in the lens opening.
It is therefore especially desirable to produce an eyeglass frame mount which will grasp eyeglass frames in such a way as to ensure that they are securely retained, with a minimum of distortion in the shape of the lens openings.
Eyeglass frames are inherently irregular and variable in their shape. It is known in the prior art to build a vise or gripping device with a composite or sectional jaw assembly that can grasp and retain an irregularly shaped object. The jaws in such variable contour vices have generally been formed from a series of slideably advanceable jaw elements constituted by parallel pins or plates. Patents covering vices in this category include United States patent in a number of categories, as follows:
(a) 2,736,936; 4,239,199 PA1 (b) 4,284,267; 3,868,102; 2,399,824; PA1 (c) 2,518,867; and PA1 (d) 626,427; 1,499,989; 2,486,494; 2,658,418; 2,754,708;
In all of these references an irregularly shaped object is retained by moving a number of parallel, separately slideable pins, bars or plates, up into contact with the outside surface of the object. In this position the retaining ends of each of these sliding elements collectively produce a contour which confirms substantially to the outside shape of the object to be grasped.
Once the object to be grasphed is fully embraced by the sliding elements, it is necessary that these elements be locked, or at least partially stabilized, in position. This is accomplished variously by the use of resilient means, such as mechanical springs (a above) that thrust the individual elements forward; by pneumatic or hydraulic cylinders (b above); by the friction of a threaded support (c above), and by positive clamping systems (d above).
Where resilient constraining means are used to hold the sliding elements in position, there is always the risk that the object being grasped will not be firmly held. Where the resilient forces are increased in order to reduce this tendancy, as by the use of stiffer springs, there is a risk that the sliding elements may distort the shape of objects that are fragile or delicate. By way of contrast, a positive clamping system ensures immobilization of the sliding elements without necessarily applying excessive compressive forces to the object being grasped.
The patents referenced earlier that contain positive clamping elements (category (d)) all rely on a "lateral" or transverse clamping system. This system relies on applying a compressive force to the sliding elements, clamping them together transversely, across the array of elements, so as to collectively immobilize them. An advantage of this system is that all of the sliding elements experience the same clamping force. This transverse method of clamping provides a positive state of immobilization for the sliding elements, to a degree not present in resilient stabilization mechanisims. But it also has the characteristic of slightly compressing the sliding members after the clamping force is applied.
The result of applying a compressive force to an array of sliding elements is to tend to displace the sliding elements together. If the elements have previously been precisely positioned to grasp a fragile object, the use of this type of immobilization system will displace the ends of the sliding elements towards each other and distort, however so slightly, the shape of the object being grasped.
In the case of eyeglass frames, it is necessary to similtaneously grasp and retain both lens openings. If a single transverse clamping system were to be used in conjunction with a series of slidable jaw elements, the effect of the clamping force would displace both lens openigns towards each other. This would produce a distortion in the shape of the frame defining the lens openings.
A means is therefore required for providing a clamping mechanism for immobilizing the sliding elements in the jaws of a variable contour vice adapted to constrain eyeglass frames where the clamping of the sliding elements has a minimum tendancy to displace such elements from their ideal locations.